Electroluminescent photoconductive display device



Dec. 21, 1965 NARKEN ET AL 3,225,253

ELECTROLUMINESCENT PHOTOCONDUCTIVE DISPLAY DEVICE Filed Dec. 28. 1961 2 Sheets-Sheet 1 FIG. 1 10 FIG. 2

Pm H

52 40 FIG 6 INVENTORS BERNT NARKEN ALLAN s MILLER 56 58 40 FIG. 5 BY MQZBM ATTORNEY Dec. 21, 1965 a. NARKEN ET AL ELECTROLUMINESCENT PHOTOCONDUCTIVE DISPLAY DEVICE 2 Sheets-Sheet 2 Filed Dec. 28. 1961 FIG. 7

United States Patent 3,225,253 ELECTRQLUMINESCENT PHOTUCGNDUETIVE DISPLAY DEVICE Bemt Narken and Allan S. Miller, Poughireepsie, N.Y.,

assignors to International Business Machines Corporation, New York, N.Y., a corporation of New York Filed Dec. 28, 1961, Ser. No. 162,896 12 Claims. (Cl. 31.5--tl) This invention relates to an electroluminescent device, and more particularly, to an electroluminescent phosphor screen suitable for use as an information display screen.

Electroluminescent panels utilized as information display screens consist of a phosphor layer composed of electroluminescent phosphor material sandwiched between a system of crossed grid conductors or strips. The conductors on opposite sides of the layer are arranged perpendicularly to each other, with the ends of the conductors of each set respectively being connected to a distributor switch. The connections between the individual conductors and the switch are such that, at any time, only one conductor of each set is connected to a source of signal voltage such as a video amplifier. As the conductors are progressively energized, light is emitted by the phosphor at the point where the particular conductors being energized cross or intersect.

A voltage pulse applied to a given two intersecting conductors is not restricted to the intersection but is also present, though in reduced intensity, along the entire lengths of the two conductors. One-half of the voltage applied at the intersection of the connected conductors appears between the unconnected and connected conductors, respectively. This half voltage is of sufiicient intensity to excite the phosphor material to an extent which makes the difference between highlight and lowlight hardly discernible. This phenomenon is called, cross-talk.

A general approach toward solving this problem has been to increase the electroluminescent non linearity characteristic by placing non-linear elements or devices in series with the electroluminescent layer. A number of non-linear elements have been suggested, for example, symmetrical varistors, ferroelectrics, and polaristors. None of these have been absolutely successful, because the basic ditficulty has not been solved but its effect merely reduced somewhat. The cross-talk condition remains ever present.

Further, the number of individual conductors in the crossed-grid network of the prior art device limits the resolution of the displayed image. The conductors must be themselves narrow in width and have a small space between them to provide the best resolution possible. Special techniques are, therefore, required to fabricate these fine conductors in the crossed-grid structure.

It is an object of this invention to provide an electroluminescent display device capable of infinite resolution in at least one direction.

It is a further object of this invention to provide an electroluminescent display device capable of absolute suppression of cross-talk and thus, producing high picture contrast.

It is a still further object of this invention to provide an electroluminescent display device capable of absolute suppression of cross-talk and which is readily adaptable to display devices in shapes other than planar.

These and other objects are accomplished in accordance with the broad aspects of the present invention by replacing at least one of the grid networks from the prior art device with another structure. A photo conductive layer is mounted substantially parallel and adjacent to the electroluminescent layer. A means for establishing electrodes across the electroluminescent layer in each of two directions is associated with the electroluminescent and photoconductive layers. This may include a plurality of spaced, transparent conductors on the side of the electroluminescent layer opposite to the photoconductive layer. A narrow width beam or strip of light irradiates the photoconductive layer in a scanning fashion perpendicular to the plurality of spaced conductors. The action of the narrow beam of light upon the photoconductive layer produces an effective electrode of the width of the beam which continuously moves over the electroluminescent layer. When an alternating current voltage is connected across one conductor and an electrical connecting means on the photoconductive layer, an electrical circuit is selectively completed through the electroluminescent layer. Light emission is observed only at the intersection of the transparent conductor and the light beam photoconductive electrode on the electroluminescent layer.

Absolute suppression of characteristic cross-talk is now a reality. The novel combination of this invention requires a single grid of parallel conductors rather than a crossed-grid network. A voltage pulse applied to the electrical connecting means is restricted, in effect, to the intersection of the transparent conductor and the light beam photoconductive electrode. There can be no other location on the screen illuminated at a given time, because only one conductor is energized at a time. An ima e may thus be produced on the novel display device having superior contrast properties to the prior art devices.

A continuous transparent conductive electrode on the electroluminescent layer opposite to the photoconductive layer can be used rather than the conductor grid structure. In this case, the photoconductive layer is alternately scanned in the horizontal and vertical planes with a narrow beam of light. This produces two electrodes of the width of the beam continuously moving over the electroluminescent layer, one electrode moving in the horizontal plane and the second in the vertical plane.

Infinite resolution is obtained from use of the alternate light scanning technique. The light beam electrodes move continuously over the electroluminescent phosphor layer. There are no spaces between electrodes as found with the crossedgrid of metal conductor structure to reduce resolution.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of the preferred embodiments of the invention, as illustrated in the accompanying drawings.

In the drawings:

FIGURE 1 is a sectional view of a first embodiment of this invention;

FIGURE 2 is a sectional view taken along line 22 of FIGURE 1;

FIGURE 3 is a plane view of the FIGURE 1 display device as seen from the photoconductive layer side;

FIGURE 4 is a plane view of the FIGURE 1 display device as seen from the electroluminescent layer side;

FIGURE 5 is a plane view of a second embodiment of the display device as seen from the photoconductive layer side:

FIGURE 6 is a sectional view of FIGURE 5 taken along line 6-6;

FIGURE 7 is a perspective view of the FIGURES 1-4 display device illustrating how it may be used to simultaneously display images in each of four directions;

FIGURE 8 illustrates the display device of the first embodiment in a disc-shaped configuration with the electro luminescent and photoconductive layers partially removed;

FIGURE 9 illustrates the display device of the first embodiment in a cylindrical configuration with the electroluminescent and photoconductive layers partially removed; and,

FIGURE illustrates the display device of the first embodiment in a spherical configuration with the electroluminescent and photoconductive layers partially removed.

Referring now, more particularly, to FIGURES 1 and 2, there is shown an electroluminescent display device or screen which comprises a substrate 10 preferably made of glass, a grid of spaced parallel conductors 12, an electroluminescent layer 14 and a photoconductive layer 16, in that order. The conductors 12 are transparent and separated by insulating areas as shown in FIGURE 2. Both the electroluminescent layer which covers the substrate and the conductors, and the photoconductive layer which is deposited over the electroluminescent layer are continuous layers. Two electrical connecting means which may be in the form of bus bars 18 are on opposite edges of the photoconductive layer and parallel to the trans parent conductors 12. These electrical connecting means serve as connecting strips to the photoconductive area and also as the power source connection.

The operation of the device may be readily understood with reference to FIGURES 1, 3 and 4. An irradiating means 20 irradiates the photoconductive layer 16 with a scanning narrow width beam or strip of light 22 which stretches in length at least between the two bus bars 18. The illuminated area of the photoconductive layer is an effective electrode of the width of the beam superimposed upon the electroluminescent layer 14. The conductive strips 12 on the substrate which are perpendicular to the beam of light are the bottom electrodes. When an alternating current voltage source 24 is connected across one bottom electrode strip 12' and the connecting bus bars, light emission is observed only at the intersection of the bottom and photoconductive electrodes. The light beam 22 can now be made to sweep or scan across the whole panel while different transparent conductive electrodes 12 are selectively connected as required during sweep to construct an image. Repetitive scanning is required for a sustained or moving image.

Another analogous display screen is shown in FIG- URES 5 and 6. This display device comprises a substrate 30, a continuous, transparent conducing electrode 32, an electroluminescent layer 34, a photoconductive layer 36, in that order. The electroluminescent and photoconductive layers are both continuous. Conducting electrodes or bus bars 38 are deposited on the edges of the four sides of the photoconductive layer in nonconnecting relationship. The continuous conducting or bottom electrode 32 does not continue to the edge of the substrate as in the first embodiment. The bottom electrode is connected to a source of ground or reference potential through a hole 40 in the substrate or alternatively at one corner of the device.

In operation, one opposite pair of bus bars 38 is connected to a positive direct current potential and the other pair of bus bars to a negative direct current potential. The value of the potentials is such that if one alternated to ground, it would not be sufficient to light the electroluminescent layer, providing a narrow width bear or strip of light irradiated the photoconductivelayer. However, an alternation between the positive and the negative potentials would cause the electroluminescent layer to emit light.

To select an area for electroluminescent emission, a light scanning means 42 scans the photoconductive layer 36 alternately in the horizontal and vertical planes with a narrow width beam or strip of light. Each light beam connects the two opposite bus bars 38 thereby establishing the potential of the bus bars applied to the bus bars along the entire beam irradiated area of the photoconductive layer. The photoconduc-tor area which was irradiated by both perpendicular beams of light has then been subjected alternately to a positive and a negative direct current potential. Light emission will thereby occur at this area location of the electroluminescent layer. For maximum light output in the FIGURES 5, 6 embodiment a non-linear layer, preferably silicon carbide, between the electroluminescent layer and the photoconductive layer should be used.

FIGURE 7 illustrates how readily the planar screens of the FIGURES 1 through 4 or FIGURES 5 and 6 cmbodiments may be adapted for display in more than one direction. Display screens of the FIGURES 1 through 4 embodiment are shown at 50, 51, 52 and 53. Each of the display screens operates in a manner as described in the earlier paragraphs of the specification. A centrally located four-sided mirror 54 is attached to shaft 56 which is driven at a uniform rate. Light sources 58 illuminate the mirror surfaces as the mirror is rotated. Light is reflected from each of the four surfaces of the mirror in the shape of a narrow beam 60 which moves as the mirror rotates across each of the display screens.

The disc-shape ddisplay device of FIGURE 8 is basically the devic eof the first embodiment of FIGURES 1 through 4. The device comprises a disc-shaped substrate 62, a plurality of spaced transparent conductors 64, an electroluminescent layer 66 and a photoconductive layer 68. A pair of circular electrical connectors or bus bars 70 are positioned concentrically on the photoconductive layer 68. One bus bar is of a diameter smaller than the inside conductor and the other bus bar is of a larger diameter than the outside conductors. A self-contained light irradiating means 74 is rotated on a shaft 76. The light irradiated means 74 applies a narrow beam of light onto the photoconductive layer as the irradiating means rotates over the disc-shaped device.

An application of the disc-shaped screen is the radar system indicator for plotting range radially against the position in azimuth or bearing. The sweeping radar beam is synchronized with the moving light irradiating means 74. Distance marking is accomplished with the transparent concentric electrodes or conductors 64 descending from the center. When a video signal is connected across one bottom conductor 64 and the connecting circular bus bars 70, by means of the light beam illuminating the photoconductive layer 68, light emission is observed only at the intersection of the bottom and photoconductive electrodes.

FIGURES 9 and 10 show further extensions of the principle of the first embodiment. Each has a self-contained light source 30 which has at least one narrow opening to allow emission of a narrow beam of light. The light source SIB rotates on a shaft 82. The substrate 84, in the case of FIGURE 9, is in the shape of a cylinder while, in the case of FIGURE 10, the substrate is in the shape of a sphere 86. The grid of spaced parallel transparent conductors, in the ease of FIGURE 9, is in the shape of a cylinder 88, while in the case of FIGURE 10, the grid of conductors is in the shape of a sphere. Over the transparent conductors in each figure is deposited an electroluminescent layer 92 followed by a photoconductive layer 94. A pair of circular electrical connections or bus bars 96 are positioned on the opposite ends of the photoconductive layer in both FIGURES 9 and 10.

The light irradiating means utilized with the display screen can be any one of a number of possible devices. It can take the form of an illuminated mirror device such as shown in FIGURE 7. Another possibility is a rotating device having a self-contained light source of the type illustrated in FIGURES 8, 9 and 10. Where a very large planar or disc display is desired, a movie projector with a continuous film having panels which will give a moving light beam is an effective device. The projector and continuous film combination would be very useful when alternating perpendicular light beams are required. A still further technique would be to use another electroluminescent source with narrow emitting strips that can be individually energized.

The photoconductive layer of the display screen" may be made of any of the well-known materials having a variable impedance characteristic in response to light energy. Examples of the photoconductor materials are cadmium sulfide and cadmium selenide.

The electroluminescent layer may comprise any of the well-known electroluminescent phosphors, embedded in dielectric binder. Zinc sulfide activated by copper and zinc selenide activated by manganese are examples of suitable phosphors. Ethyl, cellulose glass and polystyrene are examples of binders.

The conductors must be transparent, preferably a metal or metal oxide. They are illustrated as few in number and spaced a considerable distance apart for clarity of illustration. An actual screen, however, can have as many as a hundred or more conductors to the inch. The layer of conductors may be prepared by depositing onto a masked substrate a metal or a metal oxide, such as tin oxide, aluminum, silver or nickel. The mask configuration allows deposit of the conducting material onto the desired areas of the substrate. The conductors may alternately be applied in the form of a paste onto the substrate to originally construct a series of parallel conductor lines.

The cylindrical display screen of FIGURE 9 and the spherical display screen of FIGURE 10 can be fabricated in parts. That is, the cylindrical or spherical glass substrate may be cut into sections and in their sectional form have applied the conductors to the substrate surface, followed by a deposited layer of electroluminescent material, then by the photoconductive layer and finally the deposit of the bus bar areas. The sections can then be placed together and joined.

The invention thus provides an electroluminescent display device or screen capable of displaying a composite picture and having infinite resolution in at least one direction. The invention also provides a display device in which absolute suppression of crosstalk is possible. Furthermore, the novel combination of elements makes the display device system so flexible that rather than being confined to planar display screens as in the prior art, displays of disc, cylindrical and spherical configurations are readily possible. There is no size limitations and different size modules can be interchanged without change in driving requirements.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention. H i

What is claimed is:

1. An electroluminescent display screen capable of producing light images in response to electrical signals comprising: a photoconductive layer; an electroluminescent layer mounted adjacent to said photoconductive layer; and means for establishing electrodes across the said electroluminescent layer in each of two directions which are at right angles to one another; said means for establishing electrodes including a means for irradiating the photoconductive layer with a scanning narrow width strip of light which stretches in length substantially from one end of the said photoconductive layer to the other end of said photoconductive layer whereby an electrode of the width and length of the strip of light continuously moves over the electroluminescent layer.

2. An electroluminescent display screen capable of producing light images in response to electrical signals comprising: photoconductive layer; an electroluminescent layer mounted adjacent to said photoconductive layer; and means for establishing electrodes across the said electroluminescent layer in each of two directions which are at right angles to one another; said means for establishing electrodes including a plurality of spaced transparent conductors on the side of the said electroluminescent layer opposite to said photoconductive layer and means for irradiating the photoconductive layer with a scanning nan row width strip of light which stretches in length substantially from one end of the said photoconductive layer to the other end of said photoconductive layer whereby an electrode of the width and length of the strip of light continuously moves over the electroluminescent layer.

3. An electroluminescent display screen capable of producing light images in response to electrical signals comprising: a photoconductive layer; an electroluminescent layer mounted adjacent to said photoconductive layer; means for establishing electrodes across the said electroluminescent layer in each of two directions which are at right angles to one another; said means for establishing electrodes including a means for irradiating the photoconductive layer with a scanning narrow width strip of light which stretches in length substantially from one end of the said photoconductive layer to the other end of said photoconductive layer whereby an electrode of the width and length of the strip of light continuously moves over the electroluminescent layer; and means for selectively completing an electrical circuit through one end of said elec trodes and said electroluminescent layer.

4. An electroluminescent display screen capable of producing light images in response to electrical signals comprising: a planar photoconductive layer; a planar electroluminescent layer mounted parallel and adjacent to said photoconductive layer; means for establishing electrodes across the said electroluminescent layer in both the horizontal and the vertical planes; said means for establishing electrodes including a means for irradiating the photoconductive layer with a scanning narrow width strip of light which stretches in length substantially from one end of the said photoconductor layer to the other end of said photoconductor layer whereby an electrode of the Width and length of the strip of light continuously moves over the. electroluminescent layer; and means for selectively completing an electrical circuit through one end of said electrodes and said electroluminescent layer.

5. An electroluminescent display screen capable of producing light images in response to electrical signals comprising: a plurality of spaced transparent conductors; a continuous electroluminescent layer positioned over said conductors; a continuous photoconductive layer positioned over said electroluminescent layer; a pair of bus bars positioned on opposite edges of the said photoconductive layer; means for selectively connecting an AC. voltage across said conductors and the said pair of bus bars; and means for irradiating the photoconductive layer with a scanning narrow width strip of light which stretches in length at least between the said pair of bus bars where by an electrode of'th-e width and length of the strip of light continuously moves over the electroluminescent layer.

6. An electroluminescent display screen capable of producing light images in response to electrical signals comprising: a planar photoconductive layer; a planar electroluminescent layer mounted parallel and adjacent to said photoconductive layer; means for establishing electrodes across the said electroluminescent layer in both the horizontal and the vertical planes; said means for establishing electrodes including a grid of spaced parallel transparent conductors on the side of said electroluminescent layer opposite to said photoconductive layer and a means for irradiating the photoconductor layer with a scanning narrow width strip of light which stretches in length substantially from one end of the said photoconductive layer to the other end of said photoconductive layer whereby an electrode of the width and length of the strip of light continuously moves over the electroluminescent layer; and means for selectively completing an electrical circuit through one end of said electrodes and said electroluminescent layer.

'7. An electroluminescent display screen capable of producing light images in response to electrical signals comprising: a grid of spaced parallel transparent conductors; a continuous electroluminescent layer positioned over said conductors; a continuous photoconductive layer positioned over said electroluminescent layer; a pair of bus bars positioned on opposite edges of the said photoconductive layer; means for selectively connecting an A.C. voltage across said parallel conductors and the said pair of bus bars; and means for irradiating the photoconductive layer with a scanning narrow width strip of light which stretches in length at least between the said pair of bus bars whereby an electrode of the width and length of the strip of light continuously moves over the electroluminescent layer.

8. An electroluminescent display screen capable of producing light images in response to electrical signals comprising: a planar photoconductive layer; a planar electroluminescent layer mounted parallel and adjacent to said photoconductive layer; means for establishing electrodes across the said electroluminescent layer in both the hori zontal and the vertical planes; said means for establishing electrodes including a transparent conducting electrode on the electroluminescent layer opposite to said photoconductive layer and a means for scanning the photoconductive layer alternately in the horizontal and vertical planes with a narrow width strip of light which stretches in length substantially from one end of the said photoconductor layer to the other end of said photoconductor layer whereby two electrodes of the width and length of the strip of light continuously move over the electroluminescent layer, one electrode moving in the horizontal plane and the second in the vertical plane; and means for selectively completing an electrical circuit through one end of said electrodes and said electroluminescent layer.

9. An electroluminescent rectangular display screen capable of producing light images in response to electrical signals comprising: a continuous transparent conducting electrode layer; a continuous electroluminescent layer positioned over said electrode; a continuous photoconductive layer positioned over said electroluminescent layer; a bus bar positioned on each edge of said photoconductive layer; means for connecting two opposite bus bars to a positive DC. potential; means for connecting the remaining two opposite bus bars to a negative DC. potential; and means for scanning the photoconductive layer alternatively in the horizontal and vertical planes with a narrow width strip of light which stretches in length at least between the said opposite bus bars, whereby two electrodes of the width and length of the strip of light continuously move over the electroluminescent layer, one electrode moving in the horizontal plane and the second electrode in the vertical plane.

10. An electroluminescent display screen capable of producing light images in response to electrical signals comprising: a plurality of spaced parallel concentric transparent conductors; a continuous disc-shaped electroluminescent layer positioned over said conductors; a continuous disc-shaped photoconductive layer positioned over said electroluminescent layer; a pair of circular bus bars positioned concentrically on the said photoconductive layer wherein one bus bar is inside the conductor of the smallest diameter and the other bus bar is outside the conductor having the largest diameter; means for selectively connecting an AC. voltage across said parallel conductors and the said pair of bus bars; and means for irradiating the photoconductive layer with a scanning narrow width strip of light which stretches in length at least between the said pair of bus bars whereby an electrode of the width and length of the strip of light continuously moves over the electroluminescent layer.

11. An electroluminescent display screen capable of producing light images in response to electrical signals comprising: a grid of spaced parallel transparent conductors in the shape of a cylinder; a continuous cylindrical electroluminescent layer positioned adjacent to and within said conductors; a continuous cylindrical photoconductive layer positioned adjacent to and within said electroluminescent layer; a pair of circular bus bars positioned on opposite ends of the said photoconductive layer; means for selectively connecting an AC. voltage across said parallel conductors and the said pair of bus bars; and means for irradiating the photoconductive layer with a scanning narrow width strip of light which stretches in length at least between the said pair of bus bars whereby an electrode of the width and length of the strip of light continuously moves over the electroluminescent layer.

12. An electroluminescent display screen capable of producing light images in response to electrical signals comprising: a grid of spaced parallel transparent conductors in the shape of a sphere; a continuous spherical electroluminescent layer positioned adjacent to and within said conductors; a continuous spherical photoconductive layer positioned adjacent to and within said electroluminescent layer; a pair of circular bus bars positioned on opposite ends of said photoconductive layer; means for selectively connecting an AC. voltage across said parallel conductors and the said pair of bus bars; and means for irradiating the photoconductive layer with a scanning narrow width strip of light which stretches in length at least between the said pair of bus bars whereby an electrode of the width and length of the strip of light continuously moves over the electroluminescent layer.

References Cited by the Examiner UNITED STATES PATENTS 2,773,992 12/1956 Ullery 250213 2,851,634 9/1958 Kazan.

2,896,087 7/1959 Kazan 250-213 2,905,830 9/1959 Kazan 250213 2,930,897 3/1960 Livingston 250--213 2,944,155 7/1960 Mayer 250213 3,015,036 12/1961 Butler 250-213 3,042,834 7/1962 Nicoll 250-213 X 3,046,540 7/1962 Litz et al 250-213 3,102,970 9/1963 Haskell et al. 315169 GEORGE N. WESTBY, Primary Examiner.

ARCHIE R. BORCHELT, RALPH G. NILSON,

Examiners. 

1. AN ELECTROLUMINESCENT DISPLAY SCREEN CAPABLE OF PRODUCING LIGHT IMAGES INRESPONSE TO ELECTRIAL SIGNALS COMPRISING: A PHOTOCONDUCTIVE LAYER; AN ELECTROLUMINESCENT LAYER MOUNTED ADJACENT TO SAID PHOTOTCONDUCTIVE LAYER; AND MEANS FOR ESTABLISHING ELECTRODES ACROSS THE SAID ELECTROLUMINESCENT LAYER IN EACH OF TWO DIRECTIONS WHICH ARE AT RIGHT ANGLES TO ONE ANOTHER; SAID MEANS FOR ESTABLISHING ELECTRODES INCLUDING A MEANS FOR IRRADIATING THE PHOTOCONDUCTIVE LAYER WITH A SCANNING NARROW WIDTH STRIP OF LIGHT WHICH STRETECHES IN LENGTH SUBSTANTIALLY FROM ONE END OF THE SAID PHOTOCONDUCTIVE LAYER TO THE OTHER END OF SAID PHOTOCONDUCTIVE LAYER WHEREBY AN ELECTRODE OF THE WIDTH AND LENGTH OF THE STRIP OF LIGHT CONTINUOUSLYMOVES OVER THE ELECTROLUMINESCENT LAYER. 